Hobbing type gear grinder



Jan. 6, 1970 ALRIlcKENMANN HOBBiNG TYPE GEAR GRINDER 9 Sheets-Sheet 1Fild Feb.- 1, 1966 m Qwm QN mm a M R a :2?! m R mm x mm v a 8 on i mJan. 6, 19:70 A. RICKENMANN 3,487,585

l-iBB ING TYPE GE'AR GRINDER 9 Sheets-Sheet 2 Filed Feb. 1, 1966 NutJan. 6, 1970 A. RICKENMANN' ,585

HOBBING TYPE GEAR GR I NDER 9 Sheets-Sheet 5 Filed Feb. 1, 1966 3 w .9 m.H P L g v anja wflph K c I a U m x Q y r z \g Jam 6, 1970 A.R'ICKENMANN 3,487,585

HOBBING TYPE GEAR GRINDER Filed Feb. 1, 1966 9 Sheets-Sheet 4 r -N59 92%g,

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Jan. 6, 1970 4 A. R'ICKENMANN HOBBING TYPE GEAR GRINDER 9 Sheets-Sheet 5Filed Feb. 1, 1966 w mm Filed Feb. 1, 1966 Jan; 6, 1970 A. RICKENMANN3,487,585

@IOBBING TYPE GEAR GRINDER I 9 Sheets-Sheet 6 Fig. 10

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A.- RICKENMANN HQBBING TYPE GEAR GRIN-DER Fig. 17

9 Sheets-Sheet 7 Jan. 6, 1970 A. RICKENMANN 3,487,585

HOBBING TYPE GEAR GRINDER Filed Feb. 1, 1966 9 Sheets-Sheet 8 Fig. 22

Fig 23 Jan; 6, 1970 A. RICKENMANN 3,487,585

HO-BBING TYPE GEAR GRINDER Filed Feb. 1, 1966 Q'Sheecs-Sheet 9 UnitedStates Patent 3,487,585 HOBBING TYPE GEAR GRINDER Alfred Rickenmann,Zurich, Switzerland, assignor to Reishauer A.G., Zurich, SwitzerlandFiled Feb. 1, 1966, Ser. No. 524,030 Claims priority, applicatitguGermany, Feb. 4, 1965,

Int. (:1. B24b 3/12, 5/00, 9/00 US. Cl. 51-95 4 Claims ABSTRACT OF THEDISCLOSURE This invention is for improvements in or relating to hobbingtype gear grinding machines in which a workpiece being machined is inthe contact with a grinding hob while being ground. In conventionalcutting the hob has the form of a worm.

There are two ditferent forms of driving mechanism for gear grindingmachines of the kind specified. First, there are machines in which thehob and the workpiece are driven by a common power source. Second, thereare machines in which the drive is provided by two synchronous motors,one for the workpiece and the other for the hob. The invention is of usewith both kinds .of machines. The two'motor kind has been selected forexplaining and describing the underlying idea of the invention.

The invention relates to attachments for hobbing type gear grindingmachines, which attachments enable the machines to grind crowned andlongitudinally conical teeth as well as gears having straight flanks.

Gears are produced with crowned teeth to obviate edge contact betweenteeth, so that the elfects of minor axial errors can be minimised andthe gears run quietly. Gears having longitudinally conical teeth are notbevel gears "ice axis. The purpose of this tilting movement is to varythe center-distance between the workpiece and the hob.

Variations in center-distance which can be produced by tilting theworkpiece section are used in present-day hob'bing type gear grindingmachine to grind gears having crowned teeth. Two different methods ofproducing and controlling the tilting movement are known. In the firstmethod, a feeler or sensor which slides over a templet has imparted toit a rotation which is transmittted via linkage to the saddle as atilting movement. In the other method, hydraulic means are used; atemplet-controlled piston acts on a hydraulic copy system for producingthe tilting movement of the saddle.

In a variant of the first mentioned method the tilting movement isproduced by a cam arrangement having the cam rotatably reciprocated by agear and rack arrangement in which the rack is secured to the saddle.

The attachments described above have proved completely satisfactory ingear grinding machines designed to deal with small to medium sizeworkpieces. However, in the case of gear grinding machines which have todeal with relatively large-diameter workpieces the weight of theworkpiece is considerable and the construction of the machine must beadapted. Since the workpiece and the machine are so heavy, therefore, itmay be diflicult to produce and control accurately a tilting movementwhich for crown grinding amounts, as a rule, only to a few microns. Theabove mentioned variant has the additional disadvantage that there is aplay in the gear combinations at each reversal of the cam rotation.

In another known crown grinding attachment, a templet secured to theworkpiece carriage of the machine is connected by mechanicaltransmission means to a grinding spindle running in two eccentricbearing bushes 0r sleeves or the like. The transmission elementsconcerned comprise a number of items including a telescopic shaft andball joints. With this attachment, the position of the grinding spindlecan be altered, in conditions to be determined beforehand, to vary thecenter-distance between the hob and the workpiece. To this end, thetemplet imparts a small rotation to the eccentric bearing sleeves.However, disadvantage of this construction is that the large number oftransmission elements make it difiicult to maintain reliable controlover the very small displacements of the grinding spindle position. Ifthe gears are to be ground to present-day standards of accuracy, thetransmission means must be of high-precision manufacture and requirevery careful assembly, with consequent high costs.

Any system for obviating the disadvantages of these known crown grindingattachments must enable gears to carriage. The same performs theinfeeding movements H necessary in grinding. The rotational axis of thegrinding hob extends horizontally.

i A drum is pivotally mounted in the saddle and the axis of drumrotation intersects the grinding spindle axis at right-angles. Theworkpiece carriage bears the workpiece which is to be ground, and whichis clamped between two centers at either end to define an axis ofrotation. To ensure that the hob correctly forms teeth of the desiredtype on the workpiece to be ground, the drum can be pivoted into anangular position corresponding to the helix angle of the hob and to thetooth helix angle of the workpiece. The whole workpiece section which ismounted on the machine frame, i.e., the saddle including the drum,workpiece carriage and workpiece, can be tilted towards the hob aroundan axis parallel to the grinding spindle be ground with crowned andlongitudinally conical teeth by simple means, irrespective of workpieceweight and to very high precision standards.

The system of the invention to be described hereinafter is a novelsolution of the problem and which enables gears to be crown ground andconically ground by simple means. The simple construction of theinvention ensures reliability of operation and economy.

According to the invention, the saddle bearing the workpiece carriageand all the workpiece drive elements is displaceably mounted on themachine bed. The saddle is displaced by a simply constructed device, orreaction means, controlled by a templet secured to the workpiececarriage. Changes in the position of the workpiece axis which can becontrolled under predeterminable conditions can then be effected. Theresulting center-distance variations between the workpiece and thegrinding hob meet all the requirements for crown grinding and conicalgrinding.

The system according to the invention is also of use for thereciprocating grinding of gears. In reciprocating grinding therotational axis of the workpiece reciprocates continuously duringgrinding in a direction parallel to the vertical plane passing throughthe rotational axis of the grinding hob. This reciprocating movement ishorizontal and extends over a very reduced distance. In reciprocatinggrinding the lines of contact of the hob and the workpiece experiencedisplacements, with a consequent improvement in the surface texture ofthe ground tooth flanks.

For reciprocating grinding the crown grinding and conical grindingattachment according to the invention is also driven by a separate powersource, the arrangement being such that the attachments can be used justfor crown grinding and conical grinding or for reciprocating grindingalone or in combination or simultaneously.

For a better understanding of the invention and to show how the same maybe carried into effect, reference may now be made to the accompanyingdrawings wherein:

FIGURE 1 is a longitudinal section through a gear grinder according tothe invention;

FIGURE 2 is a partly sectional plan view corresponding to FIGURE 1;

FIGURE 3 is a section on the line II of FIGURE 2;

FIGURE 4 is a section on the line II--II of FIGURE 2;

FIGURE 5 is a diagrammatic view of the crowning attachment in thecentral position of the workpiece;

FIGURE 6 is a view of the central position of the workpiece;

FIGURE 7 diagrammatically shows the crowning attachment in the operativeend positions of the workpiece;

FIGURE 8 shows the top operative end position of the workpiece;

FIGURE 9 shows the bottom operative end position of the workpiece;

FIGURES 10-21 are diagrams showing the relationship between the templet(FIGURES 1013) used during the grinding of a gear and the tooth shape tobe expected from the workpiece (FIGURES 14-17) or the workpiece toothdirection diagram (FIGURES 18-21);

FIGURE 22 is a diagrammatic view similar to FIG- URE 5 but with an extraattachment for reciprocating grinding;

FIGURE 23 is a diagrammatic view similar to FIG- URE 7 but with an extraattachment for reciprocating grinding; and,

FIGURES 24 and 25 show the qualities of tooth flank which can beprovided by different operating conditions.

CONSTRUCTION OF MACHINE A saddle 2 is displaceable on the bed 1. Throughthe agency of a guide rail 4, a workpiece carriage 3 is guided on thesaddle 2 for vertical displacement and can be moved vertically byhydraulic means during grinding. The

movement can be produced, for instance, by a piston 5 moving in acylinder in the saddle 2. Two chambers 6, 7 of the cylinder can bepressurised alternately under the control of elements (not shown),according as the carriage 3 is required to move up or down.

A synchronous motor 9, hereinafter called the workpiece motor andflanged on to the saddle 2, drives the workpiece 8. A rotatably mountedcage 10 of a differential is centered in a bore in the saddle 2, thelatter bore being coaxial of the axis of the motor 9. The cage 10 islocked for grinding straight-toothed gears. A pinion 11 is disposed onthe shaft end of the motor 9 and meshes with a spur gear 12. The same isdisposed together with another spur gear 13 on a shaft 14 rotatablymounted in the cage 10. The rotation is transmitted from the pinion 13to a pinion 15 and via a shaft 16 and change gears 1720 to a pinion 21rigidly connected to a rotatable shaft 22. A spur gear 23 in engagementwith the pinion 21 is disposed on a shaft 24 rotatably mounted in thecarriage 3 and also meshes with a spur gear 25 rigidly connected to awork spindle 26. Through the agency of a dog 27, the rotations of thework spindle 26 are transmitted to a mandrel 28 and a workpiece 8secured thereto. The mandrel 28 is centered between the centers of thework spindle 26 and the quill of a tailstock 29 which can be verticallyadjusted, for instance, by operation of a handwheel 30. e

As already mentioned, the differential cage 10 is maintained stationaryfor grinding straight-toothed workpieces. To this end, a disc 33 isplaced at one end of a shaft 34 rotatably mounted in the saddle 2; thedisc 33 has a locating pin 35 engaging in a registering bore in thesaddle 2. A gearwheel 32 rigidly secured to the other end of the shaft34 meshes with a toothed ring 31 of the cage 10. Consequently, neitherthe shaft 34 nor the two gearwheels 31, 32 in engagement therewith canrotatei.e., the differential cage 10 is in a locked condition.

For grinding helical gears'an extra rotation must be imparted to theworkpiece and such rotation is provided by use of the differential, thatis, by rotation of the cage 10. To this end, the locking disc or plate33 is removed and replaced by a spur gear 36 which co-operates withthree other spur gears 37-39 to form a chain-gear set devised to suitthe requirements of the tooth angle to be formed on the workpiece 8. Thespur gear 39 is rigidly secured to a rotatably mounted shaft 41 togetherwith a spur gear 42, the latter meshing with a spur gear 43 disposed ona shaft 44 together with a bevel gear 45 meshing with a bevel gear 46disposed on a shaft 47 rotatably guided in the saddle 2. A pinion 48 issecured to the left-hand end of the shaft 47 and meshes with a toothedrack 49 screwed fast to the workpiece carriage 3.

As already stated, the piston 5 is adapted to move the carriage 3, therate of feed being determined for instance, by the quantity of oilentering or leaving the cylinder chamber 6, or 7, per unit of time. Thisquantity of oil can be varied and adapted to suit operatingrequirements.

A grinding carriage 52 is mounted on two horizontal guideways 53, 54 ofthe bed 1 and can be moved by operation of a screw-threaded spindle 56which is in turn operated by a handwheel and which meshes with a nut 57.A drum 58 is rotatably mounted in the grinding carriage 52 and has atoothed quadrant 59 meshing with a pinion 60 disposed together with ahandwheel 61 on a shaft 62 rotatably mounted in the carriage 52. Thedrum 58 can be pivoted into an angular position by rotation of thehandwheel 61. Such position depends upon the helix angle of a grindinghob 68, and, when helical gears are being ground, upon the tooth helixangle of the workpiece. The drum 58 can be pivoted to either hand sothat helically toothed workpieces of either hand can be ground.

A tangential slide 63 is disposed on that side of the drum 58 which isnear the workpiece 8. The slide or carriage 63 is displaceable on twoguideways 64, 65 and has mounted on it a grinding spindle 66 and asynchronous motor 67- which is adapted to drive the spindle 66 and whichwill hereinafter be called the grinding motor. A grinding hob 68 ofwidth W is disposed at the other end of the spindle 66. The Width W isgreater than the contact area which occurs between the workpiece 8 andthe hob profile when a gear is being ground. Shifting the slide 63enables new unused portions of the hob 68 to be used for grinding untilthe whole available width W has been dulled and the hob has to beretrued by means which are not shown. To shift the slide 63, a handwheel70' is disposed at one end of a shaft 69 rotatably mounted in the drum58, and a pinion 71 is disposed at the other end of the shaft 69. Thepinion 71 meshes with a toothed rack 72 secured to the slide 63.Consequently, rotation of the handwheel 70 moves the slide 63. After ithas been moved it is locked by means of a lever 74 on the drum 58, thelever 74 being engaged in an aperture 73.

Two adjustable abutments 95, 96 are received in a groove 85 in theworkpiece carriage 3 and co-operate with a switch 97 and with otherelectronic and hydraulic control means (not shown) to reverse thecarriage 3, the pressure in the chambers 6 and 7 changing over at eachsuch reversal.

As already stated, the saddle 2 is displaceably mounted on the bed 1.The means for shifting the saddle 2 are as follows: a shaft 76 isrotatably mounted at its top end in a bore and at its bottom end, withthe interposition of a taper roller bearing 77, in the saddle 2. At itsbottom end the shaft 76 has a pin or peg or the like which is eccentricby an amount b and which is centered in the bed 1 by means of a taperroller bearing 79. A lever 82 is rigidly secured to the shaft 76. andextends outwards through an aperture in the saddle 2. A roller 83 isdisposed on the lever 82. A groove 85 in the carriage 3 is adapted toreceive a templet such as crowning templet 86. The position thereof isso chosen that the templet 86 is adjacent the roller 83 during thevertical movements of the carriage 3. A spring 84 biases the roller 83continuously against the templet 86. Spring washers 80 are disposedbetween the bearing 79 and the base of the hole receiving the same tohelp take up backlash in the bearings 77, 79.

A taper roller bearing 90 is mounted by means of a shaft 89 in the bed 1on the right-hand side of the machine. Disposed on the shaft 89 is agearwheel 91 in engagement with a pinion 92 rigidly secured to the endof the shaft of a driving motor 93. At its top end the shaft 89 isformed with a bore which is eccentric by an amount h of the axis ofrotation of the shaft 89. A taper roller hearing 94 is received in thelatter bore and centers a straightline guide 87 which has a pin or pegor the like. Spring washers 88 act via the bearing 90, shaft 89 andbearing 94 to force the guide 87 into the guideway in the saddle 2, thushelping to take up backlash in the bearings 90, 94. Also, thespringiness provided by the spring washers 80, 88 reduces the pressurewith which the saddle 2 bears against the bed 1 and thus makes it easierto shift the saddle 2. When stationary the motor 93 is locked by a brake(not shown) so that the pinion 92 cannot be rotated. Consequently, theshaft 89 and therefore the guide 87 cannot change their positionsrelative to the saddle 2. The same can therefore move only in thedirection determined by the position of the guide 87. This directioncoincides with the extension of the straight line joining the axis ofthe workpiece 8 to the axis of the shaft 76 (see FIGURE 5)i.e., thecenter of the shaft 76 forms the axis of rotation for the saddle 2.

GRINDING PROCEDURE Consideration will now be given to the conditionslikely to arise when the machine hereinbefore described is in operation.

For the purposes of the invention, it is immaterial whether one-way ortwo-way grinding is used. In oneway grinding material is ground off theworkpiece 8 during only one direction of workpiece carriage movement forinstance during the rising movement of the workpiece carriage 3. Intwo-way grinding, grinding is performed during the rising and descendingmovements of the carriage 3. With two-way grinding, an infeedingmovement is made at the start of each stroke, by operation of thehandwheel 55 or possibly in some other way, for instance, automatically.No consideration will be given in the present context to the infeedingmovements. The machine of the invention is of use for grindingstraighttoothed and helical gears. To simplify matters, the explanationsgiven hereinafter are based on the conditions associated with grinding astraight-toothed spur gear.

Referring to FIGURE 1, during grinding the righthanded grinding hob 68is driven by the grinding motor 67 in the direction indicated by anarrow in FIGURE 1. The workpiece motor 9 drives theworkpiece 8 via thegears 11-13, 15, 17-20, the pinion 21, the two gears 23, 25 and the dog27. To ensure correct contact between the hob 68 and the workpiece 8,the drum 58 and therefore the axis of the grinding spindle 66 is tiltedinto an angular position corresponding to the helix angle of the hob 68.The same grinds material off the workpiece 8 as the workpiece carriage 3rises and descends. When the workpiece carriage 3 reaches its top orbottom end position, the respective stop 96 or 95 operates the switch97. Pressure conditions in the chambers 6, 7 therefore reverse and so,therefore, does the direction of movement of the workpiece carriage 3.The stops 95,96 are so positioned that in the top (or bottom) endposition the bottom (or top) end face of the workpiece 8 is at least ashigh or higher (or, respectively, at least as low or lower) as thehorizontal axis M-M which extends along the axis of rotation of the drum58 and passes through the center of the hob 68. The stroke or operativemovement of the workpiece carriage 3 is therefore chosen to be at leastas great as-and, as a rule, greater than-the width of the workpiece 8 tobe machined.

(a) The grinding of gears whose face is cylindrical and whose flanks arestraight in the tooth direction The tooth direction, which can bemeasured on the ground workpiece by use of appropriate instruments, willbe assumed to give a tooth direction diagram of the kind shown in FIGURE18. The roller 83 and the lever 82 rigidly connected thereto stay intheir normal position throughout the whole machining process (see FIGURE10). Consequently, the shaft 76, with its pin (FIGURE 3) eccentric bythe amount b, is not rotated, with the result that the position of thesaddle 2 relatively to the bed 1 stays stationary during grinding. Theeccentricity b of the shaft 76 and the weight component of all themachine parts on the workpiece side are so designed and so adapted toone another that the eccentric retains its selflocking action despitethe grinding pressure which is produced during grinding between the hob68 and the workpiece 8. Under these operating conditions, and providedthat the position of the grinding carriage 52 is not changed by externalaction, for instance, by rotation of the handwheel 55, during the riseand descent of the workpiece carriage 3, teeth (see FIGURE 14) whichresult in straight characteristics on the tooth direction diagram areproduced on the workpiece 8.

(b) Grinding gears whose face is cylindrical and whose flanks arecrowned A gear with a crowned flank is required to have, for instance, atooth direction diagram such as is shown in FIGURE 19. To enable such agear to be ground, a templet 86 is required which is secured in thegroove in the workpiece carriage 3. The position of the templet 86 is sochosen that the roller 83 contacts the lowest place D when the workpiece8 is in the central position relatively to the horizontal axis MM of thehob 68 (FIGURES 11 and 6). The lever 82 then has, as shown in FIGURE 5,its longitudinal axis perpendicular to the straight line joining therotational axis A of the workpiece to the eccentric axis E of thestraight line guide 87. The axis B of the bore in the lever 82, thelatter axis coinciding with the vertical axis of the shaft 76, lies onthe straight line AE. When the workpiece slide 3 rises or descends fromits central position together with the templet 86, the roller 83 of thelever 82, which is biased by the spring 84, follows the templet 86, thelever 82 pivoting anticlockwise. The resultant pivoting movement occursaround the axis C. Consequently, the axis B--i.e., the shaft 76-isdisplaced to the left-in other words, the saddle 2 connected to theshaft 76, and the workpiece 8, are shifted radially towards the grindinghob 68.

When the workpiece carriage 3 with the workpiece 8 has risen so far thatthe rotational axis of the roller 83 coincides with the plane passingthrough the bottom end face G of the workpiece 8, the roller 83 contactsthe templet 86 at a place G. During the rise of the carriage 3, theroller 83 was displaced horizontally to the right by an amount (seeFIGURES l1, 7 and 8). Associated with this shift 0 is a shift of theshaft axis B to the left by an amount d. correspondingly, the centerdistance between the hob 68 and the workpiece 8 has been reduced by theamount d.

The templet 86 shown in FIGURE 11 is symmetrical of the horizontal axisthrough D. When the workpiece 8 reaches the position shown in FIGURE 9upon the descent of the carriage 3, the roller 83 has again beendisplaced by the amount c, so that the workpiece 8 has been displacedradially towards the hob 68 by the amount d.

Assuming that there is no change in the position of the grindingcarriage 52 during the ascent and descent of the carriage 3 and that atemplet 86 shaped as shown in FIGURE 11 is used, the center distancebetween the hob 68 and the workpiece 8 is at a minimum at the places Gand F and at a maximum at the place D. More and more material is groundoff the workpiece 8 from the center D towards the ends F and G, so thatthe teeth have a corresponding barrel or crowned shape (see FIG- URE15).

Consequently, provided that appropriate templets are used, the workpiece8 can be given any desired crowning. In some gears, for instance, atooth direction diagram of the kind shown in FIGURE is requiredi.e, onlythe tooth ends are required to be crowned. The purpose of this featureis to avoid producing edge contact teeth which make an excessive noisein use. Two templets 98, 99 are used to produce teeth having crownedends. As can be gathered from FIGURE 12, the roller 8 is displaced bythe two templets 98, 99 only between the places I and H and between Kand L during the ascent and descent of the workpiece carriage 3, butstays stationary between the places I and K in just the same way as forgrinding teeth with straight flanks. Changes in center distance betweenthe hob 68 and the workpiece 8 are, as previously, associated with thedisplacements of the roller 83. Correspondingly, the teeth have straightflanks in the zone I to K and crowned flanks towards the ends H and L(see FIGURE 16).

(c) Grinding of gears having a conical face The system hereinbeforedescribed is also of use for grinding gears having a conical face andteeth which are conical lengthwise. Gears of this kind are not bevelgears in the general sense but spur gears having a slightly conical faceand a continuous profile displacement (see FIGURES 17 and 21). Theappropriate templet 100 is screwed to the workpiece slide 3 at an anglea to the direction of movement thereof, as shown in FIG- URE 13.Operation is as just described in section (b) hereof. A cone angle a isproduced on the workpiece 8, corresponding to the templet controlsurface inclined at the angle a. The angle al.6., the cone angle a ofthe workpiece 8can be varied by pivoting the templet 100.

Templets which will not be described in any greater detail herein enablegears to be ground with a conical face and crowned teeth.

In the description given so far, the control or operative surface of thetemplet 100 has geometrically simple shapes, such as an are or astraight line. If the templet 100 is appropriately shaped, in a mannernot disclosed herein, the invention can be used to produce, onstraighttoothed or helically-toothed spur gears having a cylindrical orslightly conical face, any longitudinally convex (crowned) orlongitudinally concave tooth shapes and y na ions t ereof.

(d) The reciprocating grinding of gears having a cylindrical or conicalface Reciprocating grinding is used only for finish-grinding a workpiece8. To this end, the connection between the dog 27 and'the mandrel 28 isreleased. The means and devices required for this purpose are describedand shown, for instance, in German patent specification 841,986. In thiscase, the grinding hub 68 acts as a driver and drives the workpiece 8secured to the mandrel 28. During reciprocating grinding, the workpieceis reciprocated as well as being rotatedand moved vertically.

The reciprocating motion of the saddle 2i.e., of the workpiece 8--isinitiated by starting the driving motor 93. The pinion 92 on the motorshaft drives the shaft.89 anticlockwise via the gear 91 (see FIGURE-4).The'eccentric axis E rotates anticlockwise around the axis F of rotationof the shaft 89 (see FIGURE 22). Of this rotation, only the componentwhich is perpendicular to the guide 87 is transmitted to the saddle '2.The shaft 76 with its axis B at a distance efrom the axis F of rotationof the shaft 89,'is the center around which the saddle 2 reciprocates.When the eccentric axis E has moved tothe position E and covered thedistance component 2h perpendicular to the guide 87 the straight lineAE'i.e., the saddle 2--has pivoted anticlockwise around the axis B intothe position AE'. The continuously rotating workpiece 8, whose axis ofrotation is at a distance 1 from the center B of rotation, hascorrespondingly also been shifted by the amount g. The amount ordistance g extends, as a chord of the arc AA, parallel to the verticalplane through the axis of rotation of the hob 68. As the eccentric axisE continues to rotate around the rotational axis F of the shaft 89, theworkpiece 8 reciprocates continuously.

If the fixed rotational axis B is retained, the invention can be usedwithout the lever 82, roller 83 and templet 86 for the reciprocatinggrinding of conical-face spur gears. Also, as FIGURE 23, shows, theinvention can be used in combination with crown grinding or conicalgrinding. In such cases, the rotational center B of the saddle 2 isreciprocated by an amount d through the agency of the particular templet86 used, reciprocating proceeding along the lines just outlined.

If the hob 68 and workpiece 8 are driven positivelyi.e., if there is arigid connection between, on the one hand, the Work spindle 26 andmandrel 28 and, on the other hand, the workpieces 8, the same rotatesaround the axis A. It is always the same narrow 'strips of the hobs 68which perform the grinding work on the workpiece 8. The position of suchstrips is determined by the contact relationships between the hob 68 andthe workpiece 8. These strips Wear but the other parts of the hobprofile do not get any wear. If the' strips have irregularities, such asbroken-out parts or coarse projecting grains, the surface texture of thetoothed flanks is impaired. In hob grinding, the same irregularities ofthe operative narrow strips always pass overthe same places of the toothflanks into contact with the workpiece 8' at each revolution of thehob68. Since the workpiece 8 is moved up and down along its axis ofrotation during grinding, the unevennesses caused by theseirregularities on the tooth flanks build up'cumulatively into continuousburrs or ridges extending parallel to the tooth addendum edge (seeFIGURE 24). g

In the case of reciprocating grinding, in which the workpiece 8 isreciprocated over a distance g, there is a continuous paralleldisplacement of thelines of action of the operative strips of the hob68. During this displacement new adjacent strips of the hob 68 arecontinuously being used to machine the workpiece 8. Consequently,defects on the hob or on any single strip thereof affect tooth flanksurface texture for only a fraction of the time as compared with theconditions just described. Continuous burrs or ridges on the toothflanks are reduced very considerably, only discrete protuberances orscratches being left (see FIGURE 25). Reciprocating grinding thereforeimproves tooth flank surface texture and hence makes the gear run morequietly.

The invention is of course of use in gear grinding machines in which avertical hob carriage performs the vertical reciprocation along the axisof workpiece rotation. In this case, the changes in position for crowngrinding, conical grinding or reciprocating grinding are associated withthe hob. The operation of the templet and the separate power supply areexactly the same, the templet acting via the vertical carriage andsaddle, respectively, to produce the respective necessary centerdistance changes and tangential displacements between the workpiece andthe hob. In this arrangement, the axially stationary workpiece wouldperform the infeeding movements required for grinding.

I claim:

1. A hobbing type gear grinder, comprising a machine bed, first mountingmeans on said machine bed for mounting a hob for rotation about an axis,second mounting means on said bed for mounting a workpiece for rotationabout another axis, said first and second mounting means being mountedon said bed for relative movement therebetween, said second mountingmeans comprising a saddle movable on said machine bed, a workpiececarriage slidably mounted on said saddle and supporting the workpiecefor rotation about said other axis, drive means for driving saidworkpiece carriage relative to said saddle, a templet, means on saidworkpiece carriage for securing said templet thereto, sensing meansbeing located in said saddle for following the profile of the templet,when said wo'rkpiececarriage is driven, to produce a pattern ofmovement, and reaction means on said second mounting means fortranslating said pattern of movement into an additional relativemovement between said first and second mounting means for determiningthe longitudinal profile of teeth produced on said workpiece.

2. A hobbing type gear grinder as claimed in claim 1, in which saidreaction means is located in said saddle and is connected to saidsensing means for imparting positional changes to said saddle relativeto said bed in response to the motion of said sensing means to changethe distance between the axes of rotation of the hob and the workpiecewhereby to determine the longitudinal profile of teeth produced on theworkpiece.

3. A hobbing type gear grinder as claimed in claim 2, in which saidsensing means comprises a roller, and said reaction means includes ashaft rotatably mounted in said saddle and a pin mounting said shafteccentrically in said machine bed, said shaft being acted upon by saidroller in a sense to rotate said shaft.

UNITED STATES PATENTS 2,597,648 5/1952 Lucas 5l-l00 2,786,309 3/ 1957Rickenmann.

2,839,875 6/ 1958 Rickenmann.

2,898,707 8/ 1959 Rickenmann.

3,071,897 1/ 1963 Pickener.

3,251,157 5/1966 Clark 51100 ROBERT C. RIORDON, Primary Examiner DONALDG. KELLY, Assistant Examiner US. Cl. X.R.

